1. Technical Field
The present disclosure relates generally to the treatment of respiratory and cardiovascular conditions, and more particularly, to methods and systems for continuous positive airway pressure (CPAP) therapy and the selective ramping of therapeutic pressure in a patient breathing apparatus.
2. Related Art
Sleep apnea is a serious medical condition in which patient breathing during sleep pauses abnormally, or is abnormally low. Apnea is categorized as obstructive, central, and combined obstructive and central, though the obstructive sleep apnea (OSA) is the most common. The patient's upper airway repeatedly narrows or collapses, causing pauses in breathing that may extend in duration up to half a minute. Although some degree of apnea is considered normal, in more severe cases, daytime sleepiness and fatigue may result as a consequence of reduced blood oxygen saturation, as well as constant interruptions to sleep cycles resulting from patients gasping for air. There have been studies linking sleep apnea to more severe long-term health issues including heart disease and depression, and recently, to cancer as well. With apnea being strongly linked to obesity, and with obesity being projected to increase, the number of patients suffering from sleep apnea is likely to increase concomitantly.
One common treatment for obstructive sleep apnea is continuous positive airway pressure (CPAP) therapy, where a positive pressure is applied to the patient's airway to prevent its collapse as would otherwise occur during an apnea episode. By retaining the patient's airway, normal, uninterrupted breathing during sleep is ensured. In a basic implementation, CPAP therapy applies a constant pressure that is not tied to the patient's normal breathing cycle. The positive airway pressure is desired in the inspiratory phase when the pressure differences between the lungs and the nose contribute to the collapse of the intermediate airway. Various improvements have been developed that reduce positive pressure flow to the patient during the expiratory phase, thereby reducing resistance to the patient's breathing efforts and patient discomfort. Further refinements that recognize the minimal flow and pressure toward the end of the patient's expiratory phase and responsively reduce the delivery of positive pressure have also been contemplated.
Earlier patient breathing assistance devices tended to be uncomfortable to use, not only for its bulkiness with respect to the patient interface or mask, but as mentioned above, the reduced accuracy of the control algorithms that resulted in the misapplication of patient pressure. With these issues being resolved, or at least being significantly improved upon, what was previously prescribed only for the more severe cases of sleep apnea in which the benefits of treatment outweighed the significant discomfort is now useful for treating a wider spectrum of sleep apnea conditions. Further cost reductions were possible with the elimination of expensive flow sensors and control systems based thereon in favor of pressure sensor based systems such as that described in U.S. patent application Ser. No. 13/411,257 entitled “DUAL PRESSURE SENSOR CONTINUOUS POSITIVE AIRWAY PRESSURE (CPAP) THERAPY,” filed Mar. 2, 2012, the disclosure of which is hereby incorporated by reference in its entirety herein.
Notwithstanding the increased availability of CPAP devices for home use as a result of these technical improvements and cost-saving measures, ensuring patient compliance with the prescribed treatment remains a challenge. One of the most frequent complaints, and the cause of non-compliance, is the discomfort associated with the application of pressure against the respiratory system of the patient. The additional work required during spontaneous exhalation and the forcing of air during spontaneous inhalation, may cause a suffocating sensation. Even minimal levels of pressure may be distracting enough to a patient such that merely falling asleep becomes difficult. Once in a state of sleep, however, the application of full therapeutic pressure (properly prescribed in accordance with the patient's condition) generally does not interrupt the patient's sleeping state.
In order to minimize patient discomfort during the pre-sleep state, breathing assistance devices incorporate ramping, where delivered pressure is gradually increased over a set time period. There are a variety of delivery pressure increase curves, also referred to as ramp paths, which may be implemented by the device. These include linear ramp paths, a curved ramp path that increases delivery pressure at a higher rate in the initial time period of the ramp duration, a curved ramp path that increases delivery pressure at a higher rate in the later time period of the ramp duration, and so forth. In some devices, it is possible for the patient to select between multiple available ramp paths depending preference.
Despite such improvements, even the low levels of pressure being delivered at the beginning of the ramp, which are fractions of the full therapeutic pressure, may be enough to cause discomfort for some patients. Accordingly, there is a need in the art for the selective ramping of therapeutic pressure in a patient breathing apparatus.